1. Field of the Invention
The present invention relates to a substrate layout and a heat dissipating structure of a display apparatus.
2. Description of the Related Art
In an image display apparatus using a liquid crystal panel, a light-emitting body illuminates light from a rear face of a liquid crystal panel and an image is displayed on the liquid crystal panel using the transmitted light. As the light source of a backlight that irradiates a liquid crystal panel with light from the rear face thereof, a light-emitting diode (LED) is mainly used. Heat dissipation is important in order to prevent a reduction in luminous efficiency due to heating of an LED and a reduction in life. A heat dissipation countermeasure is also required for an LED driver. Thus, a space for dissipating the heat generated by an LED and its-mounting substrate into air and a space for dissipating the heat generated by a driver and its-mounting substrate are required. In other words, a sufficient space for heat dissipation needs to be ensured, which conflicts with a request for thinning the external shape of the apparatus.
As the substrate layout and the heat dissipating structure of a conventional image display apparatus, Japanese Patent Laid-Open No. 2010-160443 discloses a method for devising the layout of a circuit substrate that is arranged on a rear face of a display panel. FIG. 7 is a cross-sectional view illustrating the configuration of a conventional image display apparatus.
A first circuit substrate 103 and a second circuit substrate 104 are arranged on the rear face of a display panel 100 such that these circuit substrates are arranged so as not to overlap each other. The component-mounting surface of the first circuit substrate 103 is arranged to face the display panel 100 (the front side) and the component-mounting surface of the second circuit substrate 104 is arranged to face the rear side of the display panel 100. The first circuit substrate 103 is arranged above the second circuit substrate 104, and a heat sink 105 is fixed to the component non-mounting surface of the first circuit substrate 103. The display panel 100 and the circuit substrates 103 and 104 are covered by a bezel 101 and a rear cover 102. Air flows from a heat dissipation hole (not shown) formed in the rear cover 102 into the interior of the housing in order to dissipate the heat generated by the circuit substrates 103 and 104. The air drawn from the lower part of the housing flows to both sides of the substrate so as to cool the second circuit substrate 104 and the air on the component non-mounting surface side flows upward toward the first circuit substrate 103. Also, the air on the component-mounting surface side of the second circuit substrate 104 is discharged from the upper part thereof to the exterior of the housing. The first circuit substrate 103 is cooled by air risen from the second circuit substrate 104 at the component-mounting surface side thereof. The portion on the component non-mounting surface side of the first circuit substrate 103 is cooled by air flowed from the central portion of the housing by means of the heat sink 105 fixed to the first circuit substrate 103, and the resulting air is discharged from the upper part of the housing. In this configuration, the component-mounting surfaces of the circuit substrates arranged in a top-bottom relationship are inverted to each other so that the air passage is split into two portions. Consequently, thinning an apparatus is achieved compatible with ensuring improvement in heat-dissipation performance.
In the configuration disclosed in Japanese Patent Laid-Open No. 2010-160443, thinning an apparatus and improvement in heat-dissipation performance can be expected when a heat dissipation countermeasure is taken by the natural convection of air without using a fan. However, in recent years, the heat quantity generated by a backlight LED which is used at the rear side of a liquid crystal panel is large, and thus, a heat dissipation countermeasure by use of forced convection using a fan is more efficient. In this case, a space is required for the fan.
When heat dissipation is performed using a fan in the structure shown in FIG. 7, it is necessary that the component-mounting surface of the first circuit substrate 103 arranged at the upper part faces the display panel side and the fan is arranged at the component non-mounting surface side. Consequently, a certain thickness is required for the housing.